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Though UHPC is much stronger and more water-resistant than traditional concrete, it has proven difficult to use as a 3D printing material, due to the rate at which it hardens. At FIU, research is now set to be conducted into identifying novel UHPC formulations as well as new ways of depositing the materials that could be deployed in future civilian or military infrastructure applications.
“Just a shell of UHPC wrapped around a structure adds to its total strength,” explains Atorod Azizinamini, a Professor of Civil Engineering at the FIU College of Engineering & Computing. “The properties of UHPC allow us to make structures smaller and more lightweight. This translates to energy savings and smaller carbon footprints.”
What is Ultra-High Performance Concrete?
Also known as reactive powder concretes (RPCs), UHPCs are essentially cement-based materials with a minimum specified compressive strength of 17,000 pounds per square inch (psi) or 120 MPa. Typically composed of portland cement, reactive powders, limestone and/or quartz flour, fine sand, high-range water reducers, and water, UHPCs can feature compressive strengths of over 29,000 psi.
As such cements’ matrices are made up of fine materials, they tend to provide a dense, smooth surface, something that allows them to transfer aesthetic details once hardened. UHPCs can also be combined with metal, synthetic or organic fibers, in order to improve their flexural strength. Doing so adds a level of ductility to the materials, and allows them to safely deform under loads, even after cracking.
Previously, UHPCs have been utilized within highway and railway infrastructure projects in North America, but deploying them as 3D printing materials has proven problematic. In particular, the way the cements solidify as they’re laid down, similarly to how sidewalks are gelatinous before hardening, has proven challenging, as when layered, they can develop inconsistencies that inhibit structural integrity.
The FIU’s $3.2M cement R&D initiative
To overcome these roadblocks, a team at FIU is now seeking to determine which compositions prevent weaknesses from forming in UHPC-3D printed structures. Utilizing the US Army funding they’ve been awarded, the university’s professors aim to come up with three different printing methodologies, and an ‘ingredient list’ that allows the resulting material to be sourced locally where possible.
These three techniques are understood to include layer printing, layer spraying and a new type of extrusion 3D printing that FIU is currently patenting. If successful, it’s thought that the research could lay the groundwork for a new method of building custom structures that are better able to resist corrosion.
In future, such a technique could prove particularly useful in military applications, by allowing personnel out in the field to 3D print infrastructure like support beams for bridges on-demand. According to the FIU team, unlocking the 3D printing potential of UHPCs would also help bring construction capabilities to remote civilian sites, and constitute something of “a logistics breakthrough.”
“This is an important investment by the Army Corps towards Florida International University,” said U.S. Rep. Mario Diaz-Balart, ranking member of the Transportation, Housing and Urban Development appropriations subcommittee of the US House of Representatives. “[The project] will help maintain our defense readiness while further advancing innovation and creating jobs for our workforce in Florida.”
With concrete 3D printing continuing to be touted as a potential means of building housing and infrastructure, significant research is being conducted into optimizing the technology for these applications. Earlier this year, engineers at RMIT University and the Hebei University of Technology came up with a way of topologically optimizing 3D printed structures, and making them fully self-supporting.
Researchers at NTU Singapore have also managed to make a 3D printing concrete with recycled glass in place of sand. Through doing so, the team aims to make glass a viable concrete substitute for sand, which is becoming a scarce resource.
Elsewhere, a TU Graz team is investigating how concrete 3D printing can drive sustainability by enabling huge material savings and slashing CO2 emissions. The researchers’ work has seen them develop concrete elements that are much lighter than conventional building slabs, which they’re hoping could help offset the detrimental effects of construction.
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Featured image shows a sign outside the FIU Engineering Center. Photo via FIU.